Integrated circuits (ICs) comprising many tens of thousands of semiconductor devices including conventional complementary metal-oxide semiconductor (CMOS) transistors are a cornerstone of modern microelectronic systems. As the technology node enters into the 22 nm dimension, the specific device requirements become increasingly more stringent and CMOS transistors might not be able to accommodate to the futuristic specifications. It has long been contemplated that a change of transistor's architecture will come to address the current technology's limitations.
The single electron tunneling transistor (SET) is one of the potential novel devices which have recently received much attention due to their small size, unique device functionality and low power consumption. The SET typically transports charges across the source to the drain via nano-size single quantum dot (QD). The operation mechanism is based on the Coulomb blockade effect on a nano-scale conduction island which causes strong suppression of the tunneling charge until the island is discharged by exactly one charge.
Typically SETs are fabricated by using lithography methods to define the QD followed by reactive ion etching (RIE) to form the Coulomb islands. However, the sizes of the Coulomb islands obtainable are greatly limited by the lithography process as well as the controllability of the chemical vapor deposition (CVD) and the RIE. Other fabrication techniques that involve using implantation into SiO2 encounter difficulties to place the implanted species accurately and precisely within the miniature nano-wire structure.
The conventional single-QD-based SETs depict poor stability in the Coulomb blockade effect due to the inevitable quantum mechanical co-tunneling process. This results in a higher leakage current in such devices. Nano-crystal formation by implantation of Si into SiO2 was reported to require high implant dosages up to the order of 1016 or 1017 cm−2 and subjecting to extremely high annealing temperatures to acquire the nano-crystals formation. This contributes to device integration concerns, furthermore, ion implantation of high dosages amounts to long duration of manufacturing which affects the throughput of the fabrication process. The location of the implanted species can also be rather randomly distributed. In addition, the high annealing temperature of nano-crystals formation in SiO2 is undesirable for the advance technological node as there is need to adopt annealing processes of low thermal budget.
In view of the above discussion, there is a need for an easy to integrate and implement technique for fabricating multiple-QD-based SET devices that have better stability against the Coulomb blockade effect as well as to site the implanted species at the designated and desired location of the device.